File Content Extraction 25.1
Filter SDK .NET Programming Guide

# Refine Detection of Text Files

During text detection, File Content Extraction analyses the first 1 kB and last 1 kB of data in a document. If less than 10% of that data consists of non-ASCII characters, File Content Extraction detects the document as a text file.

However, depending on the type of documents you are working with, the default settings might not provide the desired level of accuracy. Configuration flags enable you to change the amount of data to read at the end of a file, the percentage of non-ASCII characters permitted in a text file, and whether to use or ignore the file extension to determine the document format.

## Change the Amount of File Data to Read

During format detection, File Content Extraction reads characters from the beginning and end of a file—by default, it reads the first and last 1,024 bytes of data. Large text files might contain many irrelevant characters at the end of a file, so File Content Extraction might not accurately detect the file format. You can set a configuration flag to increase the amount of data to read from the end of a file during detection.

To change the amount of data to read during detection

- In the `formats.ini` file, set the following flag in the `detection_flags` section:

      [detection_flags]
      non_ascii_chars_end_block_size=kB

  where `kB` is the number of kilobytes to read from the end of the file, from 0 to 10. The default value is 1.

  NOTE: This flag is ignored when the value exceeds the input file size.

## Change the Percentage of Allowed Non-ASCII Characters

By default, if less than 10% of the analyzed data in a document consists of non-ASCII characters, it is detected as a text file. Depending on the type of files that you are working with, changing the default percentage might increase detection accuracy.

To change the percentage of non-ASCII characters allowed in text files

- In the `formats.ini` file, set the following flag in the `detection_flags` section:

      [detection_flags]
      non_ascii_chars_in_text=N

  where `N` is the percentage of non-ASCII characters to allow in text files. Files that contain a lower percentage of non-ASCII characters than `N` are detected as text files. The default value is `10`.

## Allow Consecutive NULL Bytes in a Text File

By default, if a document contains consecutive `NULL` bytes, it is not detected as text. Depending on the type of files that you are working with, changing the default might increase detection accuracy.

To allow consecutive NULL bytes of ASCII characters in text files

- In the `formats.ini` file, set the following flag in the `detection_flags` section:

      [detection_flags]
      ascii_allow_null_bytes=1

  The default value is 0 (do not allow consecutive NULL bytes).

## Use the File Extension for Detection

Sometimes File Content Extraction detects certain file formats, such as CSV, as ASCII because of the content of the documents. In such cases, you can use the file extension to determine the document format. Using the file extension can improve detection of formats such as CSV, but might not detect text files successfully if they have incorrect file extensions.

To use the file extension for ASCII files during detection

- In the `formats.ini` file, set the following flag in the `detection_flags` section:

      [detection_flags]
      use_extension_for_ascii=1

  The default is 0 (do not use the file extension).

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Version 25.1 | Last updated January 2025

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Product: File Content Extraction 25.1

Topic Title: Refine Detection of Text Files